Two-chamber induction melting furnace and method for operating same



June 30, 1959 J. TOSTMANN 2,892,878

TWO-CHAMBER INDUCTION MELTING FURNACE AND METHOD FOR OPERATING SAME Filed Feb. 18, 1957 2 Sheets-Sheet 1 //VVE/V 70/? W 5 fay Ihu m June 30, 1959 J. TOSTMANN 2,892,373

TWO-CHAMBER INDUCTION MEL G FURNACE AND METHOD FOR OPERATI G SAME Filed Feb. 18, 1957 2 Sheets-Sheet 2 TWO-CHAMBER INDUCTION MELTING FURNACE AND METHOD FOR OPERATING SAME Johannes Tostmann, Duisburg, Germany, assignor to Demag-Elektrometallurgie G.m.b.H., Duisburg, Germany This invention refers to a method for melting metals, particularly aluminum, aluminum alloys, copper and zinc, and to a melting furnace, and more particularly to a two-chamber induction melting furnace. Conventional furnaces of this type comprise a charging chamber and a pouring chamber, these chambers being connected by at least two melting channels which are surrounded by a transformer coil. The pouring chamber has an outlet for pouring and the whole furnace is usually tiltable so that the molten metal can be poured as required. The set of melting channels connecting the two chambers is usually straight and extends substantially in horizontal direction when the furnace is in its normal position. Furnaces of this general type have been found to work satisfactorily because the molten bath is well agitated during the operation of the furnace, and on the other hand the straight melting channels can be cleaned without difliculty.

However, the capacity of such two-chamber induction furnaces is limited by the size of the melting channels and cannot be increased at will due to the limited strength of the ceramic material forming the walls of these channels. Therefore, when a larger capacity was needed in production it was customary to arrange several of such two-chamber furnaces next to each other or one behind the other with the result that either a long stretched out group of two of such two-chamber units was created containing a certain number of transformer coils and melting channels, or that a multiple furnace unit was created in which case also a certain number of transformer coils and melting channels were used.

Such an arrangement of a plurality of furnaces has however the disadvantage that the large area occupied by one furnace is greatly increased so that the losses by radiation increase considerably and also the operational volume of the furnace equipment increases considerably.

It is one main object of this invention to avoid these disadvantages whenever two-chamber induction furnaces of great capacity are required.

It is another object of this invention to provide a twochamber induction melting furnace in which a greater capacity is obtainable without however increasing the total surface of the molten mass.

It is still another object of this invention to provide for a two-chamber induction melting furnace which can be operated with greater efiiciency and with the result of obtaining a purer and more uniform melt.

With the above objects in view, a preferred embodiment of the invention'comprises'a two-chamber induction melting furnace comprising a charging chamber, a pouring chamber, conduit means connecting the charging chamber with the pouring chamber and first heating means associated with the conduit means. In addition, the melting furnace is provided with at least one additional heating means for the metal inthe charging chamber, these additional heating means including a set of channels emanating from the charging chamber and adapted nited States Patent to contain metal to be molten, connecting means being associated with these channels for permitting the establishment of an electrical connection between metal contained within the channels at a point remote from the charging chamber so that metal within the charging chamber and the channels together with said electrical connection form an electrically conductive loop. Transformer means surround said channels in a region between the charging chamber and said connecting means whereby metal in said channels will be heated upon passage of current through said transformer means so as to be molten and in turn to heat and melt the metal in said charging chamber which then will pass through said conduit means into said pouring chamber from where it may be discharged.

In another aspect of this invention, a method for melt= ing metals in a two-chamber induction melting furnace having a first set of melting channels connecting the charging chamber and the pouring chamber, and at least one set of additional melting channels emanating from the charging chamber, comprises the steps of first heating said first set of melting channels at reduced capacity while simultaneously heating said additional melting channels at full capacity so that the charge introduced into the charging chamber is rapidly melted down. After this the additional channels are heated at reduced capacity while the melting channels connecting the two chambers are heated at substantially the same capacity as previously so that the molten metal may be let stand and is properly degassed.

In case the molten metal is to be refined, the second step of the method consists in heating the additional channels at reduced capacity while the connecting channels between the two chambers are heated at full capacity.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a twochamber furnace according to the invention, having one set of additional melting channels extending laterally;

Figure 2 is a similar sectional view of a furnace according to the invention, in which one set of additional channels is provided extending laterally and another set is provided extending vertically down from the charging chamber.

As shown in Figure 1, an induction melting furnace according to the invention is provided with a charging chamber 1 and a pouring chamber 2. These two chambers are connected by at least two melting channels 3 extending substantially horizontally while the furnace is in its normal position as shown in the drawing. The heating portion in which the channels 3 are located is surrounded by a transformer coil 4. From the pouring chamber 2 a pouring outlet 8 extends, as usual, in a slanting upward direction to the pouring outlet. In the direction of each of the melting channels 3 an opening 5 for cleaning purposes is provided. This opening is closed by a stopper 6. For sake of simplicity in this drawing only one of the melting channels 3 is shown.

Opposite to where the melting channels 3 emanate from the charging chamber 1, an additional set of melting channels 9 is provided. These channels 9 extend into a separate heating unit comprising a transformer coil 10 surrounding the channels 9. Again for the sake of simplicity only one of the channels 9 is shown in the drawing. It is to be noted that the channels 9 comprise two straight ducts substantially parallel with the center line of the coil 10, and a connecting duct which is substantially at right angles to the direction of the duct 9 and which connects their outer ends with each other. The complete additional heating unit comprising the additional channels 9 and the coil 1%) is detachably connected to the furnace at 11. It is to be noted that the additional channels 9 extend from the furnace in lateral direction, and in this particular case at approximately 45 degrees inclination when the furnace is in its normal position.

The angle of incl nation of the additional channels 9 can be chosen in different ways. However, if the inclination is chosen as for example in the embodiment shown by Figure 1, then the furnace may be tilted to a certain extent so that the melting channels 3 remain filled and no metal is poured through the pouring outlet 8, while nevertheless the metal molten in the melting channels 9 returns from the melting channels 9 into the charging chamber. his is of great advantage if for instance repairs on the additional heating unit comprising the channels 9 and the coil 10 are required because then the whole unit can be removed from the furnace and repaired or replaced without interupting the heating process in the furnace or Without the necessity of letting the main furnace cool off. Also, after removing the additional heating unit as explained, the opening or openings leading from the charging chamber 1 towards the additional heating units may be temporarily closed and the whole furnace can be operated as any other normal two-chamber furnace.

It is also evident that the individual additional heating units can be used to be attached to diiferent two-chamber furnaces so as to convert the ordinary furnace into a furnace according to the invention.

With the arrangement as illustrated by Figure 1 another important advantage can be achieved. While the ordinary melting channels 3 extend almost horizontally, the additional melting channels 9 are shown extending at a rather steep angle of about 45 degrees from the charging chamber. On account of this considerable inclination the molten bath is much stronger agitated than it could be if this additional strongly inclined channel were not existent. The intensive agitation of the bath achieved by this feature results in a more rapid melting down of the metal whereby the total time for melting a charge is greatly reduced. Since the transformer coil 10 is entirely separate from the transformer coil 4, it is possible to reduce the input into the transformer coil 10 so that the channels 9 are heated with less capacity which means that after the melting process is completed the oxide skin forming on the surface of the bath will not be destroyed by too vigorous an agitation.

Figure 2 illustrates another embodiment of the invention. in this case a separate additional heating unit comprising another set of melting channels 11 and another transformer coil 12 is arranged vertically underneath the charging chamber so that the channels 11 extend in substantially vertical direction when the furnace is in its normal position. This additional heating unit operates in the same Way as described above for the laterally arranged unit. However, on account of the fact that the channels 11 extend in vertical position the agitation of the bath is still more vigorous than in the previously described case. If therefore strong and vigorous agitation is required the unit 11, 12 may be used. If a metal is being handled that requires less vigorous agitation a laterally extended unit 9, 10 may be used. Evidently, it is possible to equip a melting furnace simultaneously with a laterally extending unit 9, 19 and a unit 11, 12 mounted underneath the charging chamber 1. Then as the conditions of the material of the process demand, either the one or the other, or both additional units together may be put into operation with different effects regarding the rapidity of the melting and with respect to the degree of agitation .of the bath.

t can be seen that the combination of a conventional Eli two-chamber induction melting furnace with additional, attachable heating units as described is of great advantage because the melting time can be greatly reduced without increasing the exposed surface of the bath in the charging chamber common to all the melting channels employed in this equipment. Besides, the agitation of the bath can be very accurately controlled and adjusted to prevailing conditions.

The number of additional heating units attached to the main furnace and the direction or inclination of the additional heating channels can be chosen within the wide range of possibilities wtihout leaving the scope of the invention.

By the combination of the standard furnace with one or more additional heating units the output of the furnace is greatly increased without increasing the volume of the heating chamber. Since the additional heating units can be rapidly disassembled from the furnace to be replaced, cleaned or repaired the interruption of the actual melting and pouring process in the main furnace can be kept to very short periods whereby production overall is greatly enhanced.

The transformer coils 10 or 12 as well as the coil 4 may be designed for single phase or multi-phase operation as the case may be.

Should the demand for molten metal he small at any time, the additional heating units can be removed or disassembled from the furnace and the openings leading to the additional heating units can be closed so that then the furnace can be operated at its ordinary capacity. It should be noted that the more vigorous agitation of the bath obtained from inclined or vertical melting channels in the additional units is of particular advantage when chips are to be melted down in the charging chamber 1. The more rapid melting down of the metal under the circumstances described above in melting channels of substantial inclination operating at a considerably higher pressure than the substantially horizontal connecting channels 3 between the chambers, has the surprising effect that the well known, but very undesirable pinch effect in the substantially horizontal channels 3 can be avoided by applying the following method. During the first melting down, the additional melting channels are heated at full capacity while the substantially horizontal melting channels are heated at reduced capacity. After the melting down is completed the capacity of the additional heating units is substantially reduced so that the agitation of the bath is also reduced and a breaking of the covering oxide layer is entirely prevented. For the purpose of refining the horizontal channels are then switched to full capacity or all the channels are heated at reduced capacity so that the already melted metal can be let stand whereby the degassing is facilitated on account of the reduced agitation of the bath.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of induction furnaces and methods of melting, differing from the types described above.

While the invention has been illustrated and described as embodied in two-chamber induction melting furnaces and methods for melting metal in such furnaces, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention-and, therefore,-such adaptations should. and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of melting metals, particularly aluminum, aluminum alloys, copper and zinc, in a two-chamber induction melting furnace having a first set of melting channels connecting the charging chamber and the pouring chamber, and at least one set of additional melting channels emanating from the charging chamber, comprising, in combination, the steps of first heating said first set of melting channels at reduced capacity while simultaneously heating said additional melting channels at full capacity so that the char e is rapidly melted down; then heating said additional channels at reduced capacity While heating said first set of melting channels substantially at the previous capacity for letting the molten metal stand and for degassing the same.

2. A method of melting metals, particularly aluminum, aluminum alloys, copper and zinc, in a two-chamber induction melting furnace having a first set of melting channels connecting the charging chamber and the pouring chamber, and at least one set of additional melting channels emanating from the charging chamber, comprising, in combination, the steps of first heating said first set of melting channels at reduced capacity while simultaneously heating said additional melting channels at full capacity so that the charge is rapidly melted down; then heating said additional channels at reduced capacity while heating said first set of melting channels at full capacity for refining the molten metal.

3. A tiltable two-chamber induction melting furnace comprising, in combination, a charging chamber; a pouring chamber spaced from said charging chamber; a first heating unit located between said chambers and including a first pair of straight channels communicating at opposite ends thereof respectively with said charging and said pouring chamber adjacent the bottoms thereof, and first transformer means surrounding said first pair of channels, one of said chambers being formed with a pair of cleaning openings respectively arranged opposite said first pair of channels; plug means removably mounted in said openings for closing the same; at least one additional heating unit including a second pair of straight channels communicating at one end thereof with the other of said chambers at a location distant from said first channels and communicating at the other end thereof with each other, and second transformer means surrounding said second pair of channels, said second pair of channels being inclined to said first pair of channels so that during heating of said furnace one of said pair of channels may be brought out of communication with molten metal located in said other chamber while the other of said pair of channels remains in contact with the molten metal in the other chamber, and vice versa, so that one pair of said channels may be cleaned and repaired while heating of the metal in the furnace may be maintained through the other pair of channels and the transformer means surrounding the same.

4. A tiltable two-chamber induction melting furnace comprising, in combination, a charging chamber; a pouring chamber spaced from said charging chamber; a first heating unit located between said chambers and including a first pair of straight channels communicating at opposite ends thereof respectively with said charging and said pouring chamber adjacent the bottoms thereof, and first transformer means surrounding said first pair of channels, one of said chambers being formed With a pair of cleaning openings respectively arranged opposite said first pair of channels; plug means removably mounted in said openings for closing the same; at least one additional heating unit removably mounted on the other of said chambers and including a second pair of straight channels communicating at one end thereof with the other of said chambers at a location distant from said first channels and communicating at the other end thereof with each other, and second transformer means surrounding said second pair of channels, said second pair of channels being inclined to said first pair of channels so that during heating of said furnace one of said pair of channels may be brought out of communication with molten metal located in said other chamber while the other of said pair of channels remains in contact with the molten metal in the other chamber, and vice versa, so that one pair of said channels may be cleaned and repaired while heating of the metal in the furnace may be maintained through the other pair of channels and the transformer means surrounding the same.

References Cited in the file of this patent UNITED STATES PATENTS 761,920 Schneider June 7, 1904 2,415,974 Tama et al. Feb. 18, 1947 2,423,912 Tama et al. July 15, 1947 2,474,443 Tama et al. June 28, 1949 2,520,349 Tama Aug. 29, 1950 2,587,727 Horswell et al. Mar. 4, 1952. 2,647,305 Cook et al. Aug. 4, 1953 2,805,271 Lang Sept. 3, 1957 FOREIGN PATENTS 663,943 Great Britain Jan. 2, 1952 

1. A METHOD OF MELTING METALS, PARTICULARLY ALUMINUM, ALUMINUM ALLOYS, COPPER AND ZINC, IN A TWO-CHAMBER INDUCTION MELTING FURNACE HAVIG A FIRST SET OF MELTING CHANNELS CONNECTING THE CHARGING CHAMBER AND THE POURING CHAMBER, AND AT LEAST ONE SET OF ADDITIONAL MELTING CHANNELS EMANATING FROM THE CHARGING CHAMBER, COMPRISING, IN COMBINATION, THE STEPS OF FIRST HEATING SAID FIRST SET OF MELTING CHANNELS AT REDUCED CAPACITY WHILE SIMULTANEOUSLY HEATING SAID ADDITIONAL MELTING CHANNELS AT FULL CAPACITY SO THAT THE CHARGE IS RAPIDLY MELTED DOWN; THAN HEATING SAID ADDITIONAL CHANNELS AT REDUCED CAPACITY WHILE HEATING SAID FIRST SET OF MELTING CHANNELS SUBSTANTIALLY AT THE PREVIOUS CAPACITY FOR LETTING THE MOLTEN METAL STAND AND FOR DEGASSING THE SAME. 